International Mobile Telecom System-2000 (IMT-2000), as an advanced mobile communication system, can enable a mobile terminal to transmit, in any way, information to anyone with a high quality at anytime and anywhere on a global scale. Each mobile terminal can support various types of services simultaneously. For example, the mobile terminal can receive voice calls when it is connected to a local area network, i.e., it can perform voice communication and data reception/transmission simultaneously. In a communication system, a Core Net (CN) is a basic platform capable of providing a user with all communication services including switching of calls and routing of packet data. Therefore, logically, the CN includes Circuit Switched (CS) domain and Packet Switched (PS) domain. The function of each domain is realized by several sets of basic processes, and each of which consists of several sub-processes for achieving a set of special functions respectively. The basic process for the CS domain mainly supports CS domain services, including the sub-processes such as normal location update, periodical location update, International Mobile Subscriber Identity (IMSI) attachment/detachment, Temporary Mobile Subscriber Identity (TMSI) reallocation, authentication, encryption and identification. The basic process for PS domain mainly supports PS domain services, including the sub-processes such as General Packet Radio Service (GPRS) attachment/detachment, combined routing update, normal routing update, periodical routing update, Packet Temperate Mobile Subscription Identity (P-TMSI) reallocation, GPRS authentication and encryption. The basic processes include common processes and special processes. The common processes are initiated after signaling connection has been established, while the special processes are initiated when there exists no signaling connection and the network will judge whether or not to accept such special processes.
The inventor finds that there exists in the prior art the following problem. After the mobile terminal initiates the basic process, if the basic process is refused by the network for Reason #7 (GPRS services not allowed), the mobile terminal will set the GPRS status as GU3 Roaming Not Allowed, and delete status flag bits such as P-TMSI, P-TSMI signature, RAI and GPRS Ciphering Key Sequence Number (CKSN) in accordance with a corresponding protocol of 3GPP, e.g., TS24.0008. Moreover, before shutting down the mobile terminal or replacing a SIM card, the network is impossible to provide the SIM card with GPRS services. As a result, this will get a user of the mobile terminal into trouble in use.